This invention relates to the manufacture of a head member of a crosshead piston by casting and machining an iron blank. More particularly, this invention relates to a foundry core for molding an interior of the blank, which core also molds an exterior surface portion of the blank about a central axis so as to provide a reference for conveniently and precisely locating the axis for performing the machining operation.
A crosshead piston for a diesel engine comprises a head member pivotally connected to a separately formed skirt member. The head member comprises a combustion chamber-defining crown and a dependent annular ring belt that are symmetrical about a central longitudinal axis. In particular, it is desired that the inner wall and the outer wall of the ring belt lie concentric about the same axis. In addition, the head member comprises a skirt connection portion and a plurality of struts connecting the skirt connection portion to the ring belt and crown, which struts extend within the ring belt.
The head member is formed by casting an integral iron blank having sections corresponding roughly to the elements of the head member and machining exterior surfaces to finish the product. The blank is integrally cast in a foundry sand mold comprising a core for shaping the interior of the ring belt and the struts.
In order to precision machine the head, it is essential to determine the center axis in the blank. Despite the exercise of care in positioning the core within the foundry mold, the orientation of the core may vary. Heretofore, it has been necessary to locate upon an interior wall of the ring belt section of the blank in order to fix the center axis for the purpose of machining the exterior wall about the identical axis. Location upon the core-shaped interior ring belt wall in this manner permits the center axis to be determined relative to the interior wall, so that the finished exterior wall is machined concentric to the interior wall. However, access to the ring belt interior is cumbersome because of the presence of the struts and skirt connection portion.
Therefore, it is an object of this invention to provide a method for manufacturing a crosshead piston head member comprising casting an iron blank and machining the blank to produce the head member, which method provides an exterior, readily accessible blank surface that is precisely and reliably situated relative to the desired product axis for locating the blank for the machining operation.
More particularly, it is an object of this invention to provide a foundry core for incorporation into a foundry sand mold for casting a blank that is machinable to produce a crosshead piston head member, which core not only shapes an interior portion of the blank symmetrically about a central longitudinal axis, but also molds an exterior surface portion of the blank symmetrically about the axis. The core-molded exterior surface portion provides a readily accessible surface for determining the axis during subsequent machining operations.